The present invention relates to an automatic exposure device in camera for exposing original images on a microfilm.
In recording original images such as manuscript, photographs and documents on a microfilm, it is necessary to detect the overall density of the original images in order to expose those original images with an adequate exposure corresponding with the images.
In the prior art, sensors 2A to 2E as shown in FIG. 1 (e.g. photo sensors such as photodiodes) were provided at plural positions to measure the overall density data of the original image 1 and determine the exposure by means of a circuit as shown in FIG. 2 for exposing the original 1. Data on density (or amount of light) measured by the five sensors 2A to 2E are inputted at a switch 3, where one of the density data is selected by contact points a to e of the switch 3, converted into a digital value by an A/D converter 4 and inputted to a CPU 5 such as a micro-processor. The CPU 5 successively switches the contact points a to e of the switch 3 so as to detect all the density data from the sensors 2A to 2E. After obtaining all the necessary data on the density from the sensors 2A to 2E by means of the CPU 5, an operator manipulates keys 6 to calculate the exposure from a given operational equation. By controlling the speed of a shutter 7 which exposes the microfilm with the calculated exposure, an adequate exposure which corresponds well with the density of the original image is automatically achieved.
The conventional automatic exposure device is defective in that since plural sensors are provided and successively scanned to obtain the density data, attaching of the sensors is quite troublesome and photometric operation itself complicated, pushing up the cost.